1. Field of the Invention
The present invention relates to a compact light-weight imaging lens to be used in a camera in which a solid-state imaging device such as a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) is mounted.
2. Description of the Related Art
Recently, demands are growing for portable cameras having solid-state imaging devices, such as a digital still camera and a camera installed in cellular phone. Imaging lenses to be used in such cameras are required to be installed within limited spaces, respectively, and are thus required to be further downsized as compared with typical lenses for silver salt cameras. Further, recent and drastic advancement of higher pixelation for solid-state imaging devices has resulted in strong demands for higher optical performance.
Various imaging lenses constituted of a small number of lenses have been proposed as ones suitable for small-sized solid-state imaging devices, respectively (for example, Japanese Patent Application Laid-Open Nos. 2004-102234, Japanese Patent Application Laid-Open No. 2004-53813). Imaging lenses described in the above patent documents are each constituted of four lenses such that an aperture-stop is arranged between a first lens and a second lens.
Recent rapid improvements of technologies have also promoted downsizing of cellular phones, mobile devices, and the like. Thus, lenses to be used in such compact devices are also demanded to be downsized in outer diameter and shortened in total length. Further, advancement of higher pixelation for solid-state imaging devices such as CCD and CMOS leads to demands for higher-performance lenses to be used therefor.
When a conventional electronic shutter is used in a situation of advancement of higher pixelation for CCD, smear (phenomenon where streak-like light is caused vertically relative to an optical axis when a photograph including a strong light source such as sunlight or illumination light is taken by an imaging apparatus utilizing a CCD, for example) is caused to affect an image taken through a lens. To avoid occurrence of smear, a mechanical shutter (light-shielding plate) or the like is required. However, since the mechanical shutter has a certain thickness, the mechanical shutter is hardly used for an imaging lens installed in a cellular phone or mobile device that is required to be compact-sized.